Low-Temperature Power Plant and Process for Operating a Thermodynamic Cycle

ABSTRACT

The invention concerns a mechanism for operating a thermodynamic cycle, particularly a low-temperature power plant, as well as a related process, whereby a low-temperature mass stream ( 1 ) feeds a first heat stream to a working fluid ( 6 ) circulating in a first cycle at an initial temperature level (T 1 ), whereby subsequent to an expansion of the working fluid in an expansion machine ( 7 ) a second heat stream is extracted from the working fluid ( 6 ) at a lower expansion temperature level (T 5 ) with respect to the initial temperature level (T 1 ) for an improvement of the energy exploitation of the thermodynamic cycle or the low temperature power plant, which is pumped to a higher pump temperature level and is fed to the low temperature mass stream ( 1 ) and/or fed at least partially to the first cycle.

The invention concerns a mechanism for operating a thermodynamic cycle,particularly a low-temperature power plant, as well as a relatedprocess, whereby a low-temperature mass stream feeds a first heat streamto a working fluid that circulates in a first cycle at an initialtemperature level and whereby subsequent to an expansion of the workingfluid in an expansion machine, a second heat stream is extracted fromthe working fluid at a lower expansion temperature level relative to theinitial temperature level, especially in a cooling device.

Thermodynamic cycles of this type are used especially in low-temperaturepower plants for recovering the energy from a low-temperature massstream, for example, with a turbine, which serves as an expansionmachine. Low-temperature power plants find application, for example, ingeothermal energy, solar energy, in energy recovery from biomass, andwaste heat which is created, for example, in rotting or fermentingprocesses, i.e. in a landfill or similar. In the course of saving fossilfuels and in the course of an attempt of dispensing with such fossilfuels completely, interest in processes of this type is growingsteadily.

Based on the smaller temperature difference in the operation of athermodynamic cycle compared to a high-temperature power plant, thedegree of effectiveness of a low-temperature power plant is naturallyalways significantly lower than in a high-temperature power plant. Evenmore, as the temperature of a low-temperature mass stream is specifiedbased on circumstances, for example, a geothermal heat source or aprocess that conveys waste heat, there are attempts to improve theenergy exploitation of a low-temperature power plant with optimizationmeasures.

It is the objective of the present invention to improve the energyexploitation of operating a low-temperature power plant, especially,with only small changes to the apparatus of existing thermodynamiccycles.

According to the invention, this objective is solved by a thermodynamicmachine, particularly a low-temperature power plant with thecharacteristics of claim 1, as well as by a process for operating athermodynamic cycle, particularly a low-temperature power plant with thecharacteristics of claim 6. Advantageous embodiments and furtherdevelopments are indicated in the respective dependent claims.

In a thermodynamic machine according to the invention, particularly in alow-temperature power plant with at least one first cycle forcirculating a working fluid, the first cycle has at least one expansionmachine and at least a first heat exchanger for feeding the first heatstream from a low-temperature mass stream into the first cycle, wherebyat least one heat transformer is provided with its colder side betweenthe expansion machine and the cooling mechanism or in the coolingdevice, which is, in particular, a condenser that is in heat streamconnection with the cycle, and with its warmer side with thelow-temperature mass stream or is in heat stream connection with thefirst cycle. As heat stream connection, the heat transformer has, forexample, a heat exchanger on its colder side and on its warmer siderespectively, Preferably, this makes an increase in the degree ofeffectiveness or a heat throughput of a thermodynamic cycle possible,particularly of a low-temperature power plant. Especially, existinglow-temperature cycles can be retooled with little time and effort bythe use of a heat transformer.

For example, a water stream of geothermal brine is used as alow-temperature mass stream. At sufficient temperature of the geothermalbrine, [Note: original says “Sonde” instead of Sole=brine.] thelow-temperature mass stream can also be present in the form of steam.However, in place of water, other fluids can also be used aslow-temperature mass streams. Alternatively to a geothermal brine [Note:original has Sonde], the low-temperature mass stream can also be broughtto its application temperatures with solar heat, waste heat from biomassprocesses, waste heat from other processes or the like.

In particular, the working fluid is selected in such a way that at atemperature of the low-temperature mass stream it is present invaporized form, whereas it is present in liquid phase at one of thelower temperature levels of the cycle. Depending on the applicationtemperature, commonly used cooling agents are used, for example,pentane, butane, other hydrocarbons or the like. In a simple cycle, forexample, the working fluid is vaporized in a first step in a heatexchanger by the low-temperature mass stream, in a second step it isexpanded in a turbine that acts as an expansion machine and subsequentlyit is condensed again, so that it can be heated anew by thelow-temperature mass stream in the heat exchanger.

For example, the cycle can be operated as an organic Rankine cycle, anORC. In the process, an ORC fluid, for example, pentane, butane oranother cooling agent, is heated in a pre-heater, vaporized in avaporizer that is heated by the low-temperature mass stream, conveyed toa turbine that acts as an expansion machine and expanded there, andcooled down in a condenser so that it can be fed into the cycle anew. Inthis process, a recuperator is provided between the turbine and thecondenser which serves to recover residual heat from the exhaustemission of the turbine. The amount of heat that is generated in thisprocess is used to feed the pre-heater. In a process according to theinvention, a heat transformer is provided in addition, which extracts asecond heat stream from the working fluid subsequent to the turbine orthe expansion machine and after the recuperator and prior to a coolingdevice, which is, in particular, a condenser, and pumps such to a higherpump temperature level and again feeds it into the cycle or thelow-temperature mass stream.

With respect to the fundamentals of an ORC process, reference is made toDE 692 18 206 T2, to the entirety of which reference is made within theframework of the revelation. Preferably, use of an ORC cycle makes itpossible to retool existing systems that work according to thisprinciple at little expense to improve their degree of effectiveness.

In a different embodiment, the cycle can be operated as a Kalina cycle.In doing so, the Kalina process uses a method that is similar to an ORCprocess, whereby the working fluid is first heated, vaporized, in theexpansion machine, for example, a turbine, pressure is released, it iscondensed and subsequently conveyed to heating again. In contrast to anORC process, the working fluid in the vaporizer or desorber is splitinto a steam phase and a watery phase with a subsequent separator,whereby the steam is conveyed through the expansion machine, while thetension of the fluid phase is released after a potential recovery ofheat by a restrictor of the exit pressure of the expansion machine,particularly the turbine. Subsequently, the two partial streams areunited again and stream back through an internal heat exchanger to acondenser or absorber. After the condensation/absorption, pressure isincreased again, for example, by a feed pump. With respect to thefundamentals of an ORC process, reference is made to US 2004 0182084 A1,to the entirety of which reference is made in the revelation.

In addition to these embodiments, any type of low-temperature powerplant can be operated in accordance with the invention.

Particularly downstream of the expansion machine, a cooling device isprovided, for example, a condenser or the like, whereby the second heatstream is extracted from the low-temperature mass stream prior to or inthe cooling mechanism.

As heat transformer, a system with at least two ejector-adsorbers isused, as described in patent specification DE 34 08 192 C2, to theentirety of which reference is made within the framework of therevelation. Alternatively, a power heating machine with an at leastessentially adiabatic compression step of a working fluid can be used.

According to a further development, a second cycle, particularly an ORCcycle with a second heat transformer which is mounted in the same way asthe first heat transformer, located sequentially to the first cycle,whereby the first and second heat transformer with their warm siderespectively are in heat stream connection with the low-temperature massstream between the first and the second cycle. For this purpose, theheat transformers are, for example, respectively provided with heatexchangers at their ends, which are, for one, in heat stream connectionon the warmer side of the heat transformer with the low-temperature massstream, and for another, on the colder side of the heat transformersthey are in heat stream connection with the respective cycle. Thetemperature on the warmer side of the second heat transformer is therebypreferably lower than the temperature on the warmer side of the firstheat transformer. Preferably, the heat exchangers of the heattransformers are located in the low-temperature mass stream in such away that first the heat of the second heat transformer is given off tothe low-temperature mass stream and subsequently the heat of the secondheat transformer. Thereby, the temperature of the low-temperature massstream preferably increases stepwise upstream of the second cycle.

In a further embodiment, a second cycle is provided, which is feddownstream of the first cycle by a branch stream of the low-temperaturemass stream, whereby the first heat transformer with its warmer end isin heat stream connection with the branch stream upstream of the secondcycle and whereby a down-stream feedback of the branch stream isprovided downstream of the second cycle into the low-temperature massstream. For example, an existing heat cycle, particularly according tothe ORC principle, can be improved in its energy exploitation bycoupling it with a second heat cycle, particularly according to the ORCprinciple, so that only a feeder line must be placed from one outlet ofthe first cycle to the inlet of the second cycle and a downstream linefrom the second cycle again to the first downstream line, whereby inaddition to the basically ordinary heat cycles according to, forexample, the ORC principle, a heat transformer is used in such a waythat its warm end is in heat stream connection with the inlet line ofthe second heat cycle. Preferably, electricity exploitation can therebybe improved by approximately 15%.

In order to realize a closed low-temperature mass stream cycle, a secondcycle can be provided which shows a downstream feedback to its inlet,which is in heat stream connection with the warmer end of the first heattransformer. The first and second cycle stream separately, inparticular, they are completely separate from one another and are onlyconnected with one another in heat stream connection by the first heattransformer.

In a further development, at least one feedback line for feeding back apartial stream from the low-temperature mass stream is provideddownstream of the first cycle, whereby the warm side of the first heattransformer is in heat stream connection with this partial stream.Thereby, the low-temperature mass stream is preferably increasedupstream of the first cycle. Particularly, heat transformers andfeedback lines are to be dimensioned such that the recycled partialstream can be heated precisely to the initial temperature level, i.e.the first temperature of the low-temperature mass stream.

In another embodiment, the warm side of the first heat transformer is inheat stream connection with the first cycle in a section between thevaporizer and the expansion machine. In particular, in this section acorresponding heat exchanger is provided which is fed by the warm sideof the first heat transformer. For this reason a temperature of theworking fluid directly before entry into the expansion machine ispreferably increased and thereby the energy exploitation of theexpansion is improved.

Moreover, the invention concerns a process for operating a thermodynamiccycle, particularly a low-temperature power plant, particularlyaccording to one of the previously described embodiments in which aworking fluid circulates, to which a first heat stream is fed by alow-temperature mass stream at an initial temperature level, wherebyafter expansion of the working fluid in an expansion machine—byreleasing mechanical energy—a second heat stream is extracted from theworking fluid at a second lower expansion temperature level with respectto the initial temperature level, particularly prior to entry into acooling device, which is pumped to a pump temperature level that ishigher or equal to the initial temperature level in at least one heattransformer, and is again fed to the low-temperature mass stream and/orthe first cycle at least in part.

Advantageously, this makes an increase in the degree of effectiveness orthe heat throughput rate of the thermodynamic cycle possible,particularly of a low-temperature power plant.

The initial temperature level which corresponds to the temperature levelof the low-temperature mass stream is, for example, a temperaturebetween an ambient exterior temperature and approximately 200° C., forexample, 120° C. The pump temperature level is preferably at leastequally high, advantageously, however, higher than the initialtemperature level.

In order to pump the second heat stream to the higher pump temperaturelevel, according to a further development, a temperature of a heattransformer fluid that is heated by a second heat stream with twoejector adsorbers is raised to or above the higher pump temperaturelevel.

In the process, for example, the heat transformer fluid is driven out ofa fixed adsorption means by a relatively low first pressure, the gaseousheat transformer fluid that is created during the ejection at arelatively low first temperature is transformed into a fluid phase bygiving off heat and heat transformer fluid that is present in fluidphase at an intermediate second temperature and at a relatively higherpressure is transformed into the gaseous phase by absorbing heat, thegaseous working fluid by giving off useful heat at a relatively highthird temperature is adsorbed by a fixed adsorption means and theprocess is maintained by cyclical ejection and adsorption of workingfluid in the adsorption means or parts thereof, whereby at least twoejection adsorbers present at varying temperatures and pressuresexchange heat via heat exchange devices from the heat transformerfluid-richer to the heat transformer fluid-poorer ejection-adsorber,whereby subsequent to the heat exchange between these ejector-adsorbers,heat transformer fluid is exchanged between these ejection adsorbers bypressure adjustment, and is driven out of the heat transformerfluid-richer adsorption means by absorbing heat and is adsorbed in theheat transformer fluid-poorer adsorption means by generating heat.

In a further variation, a heat transformer fluid heated by a second heatstream is at least essentially adiabatically compressed and therebyheated to or above the pump temperature level in order to pump thesecond heat stream to the pump temperature level. A suitable coolingagent such as, for example, pentane, butane or another suitablehydrocarbon compound is used as heat transformer fluid depending on thetemperature range.

According to a further development it is provided that through a secondheat stream that is raised to the pump temperature level, a temperatureof the low-temperature mass stream or/and a temperature of the workingfluid is increased in the first cycle. Preferably, this makes anincrease of the degree of effectiveness of the thermodynamic cyclepossible, particularly the low-temperature power plant. In this process,for example, the second heat stream is pumped to the higher pumptemperature level, which lies above the initial temperature level, thetemperature of the low-temperature mass stream. In this manner, thetemperature of the low-temperature mass stream in increased. Similarly,an increase in the temperature of the working fluid can be provided atone point in the cycle. Preferably, a maximum temperature of the workingfluid is increased within the thermodynamic cycle.

Alternatively or additionally, it can be provided that thelow-temperature mass stream is increased by a partial feedback of alow-temperature mass stream outflow that is heated with a second heatstream. Preferably, the partially recirculated low-temperature massstream outflow is pumped to the same temperature level as the incominglow-temperature mass stream. It is self-explanatory that the volumestream or mass stream transported out of a geothermal source, forexample, is not changed in the process. However, as a result of therecirculation, the mass stream or volume stream that passes through thecycle is increased.

Various embodiments and procedures or arrangements can be provided forthe operation of a cycle. In a first provided process, at least twocycles, particularly ORC cycles, are sequentially fed by thelow-temperature mass stream, whereby the recirculation into thelow-temperature mass stream of the second heat streams that arerespectively pumped to the higher pump temperature level takes placebetween the first and the second cycle. Preferably, this makes anincrease in temperature of the low-temperature mass stream possiblewhich has passed through the first cycle, particularly the ORC process,and an enhanced energy exploitation of the second ORC process.

In an additional variant, at least two cycles are provided, particularlyORC cycles, whereby from the low-temperature mass stream downstream ofthe first cycle a branch stream is branched off for feeding the secondcycle, which is reunited again downstream with the low-temperature massstream downstream of the second cycle, whereby the second heat streamthat is pumped to the higher temperature level of the first cycle isconveyed to the branch stream. Advantageously, this makes an enhancementof the existing system possible by coupling in a second thermodynamiccycle, particularly an ORC cycle.

According to a further development, at least two cycles, particularlytwo ORC cycles are provided, whereby the second heat stream that ispumped to the pump temperature level of the first cycle is fed to anoutflow of the second cycle, which is fed to the second cycle again asinflow. As a result, the second ORC cycle can be designed completelyseparate from the first ORC cycle except for a heat stream connection.In this process, the heat stream is conveyed without exchanging a massstream between the two cycles.

In an additional embodiment it is provided that from the low-temperaturemass stream downstream of the first cycle a branch stream is branchedoff which is heated with the second heat stream that is pumped to thehigher pump temperature level and is fed again to the low-temperaturemass stream upstream of the first cycle.

Thereby it is provided that the branch stream is dimensioned in such away that its pump temperature level corresponds to the initialtemperature level of the low-temperature mass stream prior to beingrecirculated. In this way, the low-temperature mass stream is enlargedupstream of the first cycle. Advantageously, this leads to enhancedenergy exploitation. Simultaneously, particularly a low-temperature massstream outflow is not increased in spite of the higher low-temperaturemass stream passing through the first cycle.

In a different embodiment, the second heat stream is extracteddownstream of the expansion machine and after being pumped to the higherpump temperature level, is again fed into the first cycle particularlydirectly before the expansion machine. Preferably, a temperature in amass stream of the working fluid in the first cycle between a vaporizerand the expansion machine is thereby increased. In the process, the heatpotential in this mass stream is increased in particular.

In the following, the invention is explained using the drawing. However,the invention is not limited to the combination of characteristics shownthere. Rather, characteristics shown in the respective figures as wellas the description can be combined with one another within the frameworkof the protective area of the claims for further development.

Shown are:

FIG. 1 design of an ORG cycle according to prior art,

FIG. 2 design of a Kalina cycle according to prior art,

FIG. 3 a first embodiment of a cycle according to the invention,

FIG. 4 a second embodiment of a cycle according to the invention,

FIG. 5 a third embodiment of a cycle according to the invention,

FIG. 6 a fourth embodiment of a cycle according to the invention,

FIG. 7 a fifth embodiment of a cycle according to the invention,

FIG. 8 a sixth embodiment of a cycle according to the invention, and

FIG. 9 a seventh embodiment of a cycle according to the invention.

The design shown in FIG. 1 is a design used in a geological applicationof an ORC cycle according to prior art. For supplying a low-temperaturemass stream 1, a deep well pump 2 is provided, which transports thermalwater from a geothermal well 3 that has a temperature of 80° C. Thus thelow-temperature mass stream 1 thus provides an initial temperature levelof 80° C. and heats a working fluid 6 by means of a first heat exchanger4 in a vaporizer 5, which is brought to vaporization in vaporizer 5. Inthe embodiment according to FIG. 1, working fluid 6 is pentane. Aftervaporization, working fluid 6 is fed to a turbine 7 that acts as anexpansion machine in which vaporized working fluid 6 works and is beingreleased. In the process, the temperature of working fluid 6, whichsubsequently runs through a recuperator 8 is decreased to an expansiontemperature level. Downstream of recuperator 8, working fluid 6 runsthrough a condenser 9, in which working fluid 6 is condensed again.After condensation, working fluid 6 is fed again to vaporizer 5 bydelivery pump 10 through recuperator 8 and a pre-heater 11. In thisprocess, recuperator 8 serves to at least partially extract heatcontained in working fluid 6 after expansion in turbine 7 and feed itagain to the working fluid 6 prior to entry into pre-heater 11.

The design of a Kalina cycle according to prior art that is shown inFIG. 2 is in large part similar to the ORC design shown in FIG. 1. Alow-temperature mass stream 1 that is fed by a geothermal well 3 heats aworking fluid 6 in a desorber 12 which is then desorbed. Subsequently,this working fluid 6 is split into a steam phase 14 and a watery phase15 in a separator 13.

Ammonia mixed with water is used as working fluid 6. For this reason,the steam phase 14 is ammonia-rich steam and the watery phase 15 is anammonia-poor watery phase 15. Subsequently, the steam phase 14 isdelivered to a turbine 7 that acts as an expansion machine in whichsteam 14 is expanded and thereby work is performed. The watery phase 15is put together again with the steam phase 14 via a high temperaturerecuperator 16 and a restrictor 17 after exiting turbine 7, and conveyedagain to an absorber 19 via a low-temperature recuperator 18.Subsequently, working fluid 6 is again fed to desorber 12 by a feed pump10 via low temperature recuperator 18 and high temperature recuperator16, as well as pre-heater 11.

Based on this prior art, the invention is shown in the following byusing various variants schematically and as examples.

In a first variant as per FIG. 3, a first cycle 20 is provided which isan ORC cycle as it is shown in FIG. 1, for example. Additionally, afirst heat transformer 21 is provided which has a warmer side 22 and acolder side 23. The warm side 22 has a heat stream connection with alow-temperature mass stream 1 via heat exchanger 24. Thislow-temperature mass stream 1 has a mass stream dm₁/dt at an initialtemperature level T₁. Thereby, the initial temperature level T₁ is 120°C. After passing through heat exchanger 24, low-temperature mass stream1 has a temperature T₂, which is 126.34° C. The increase of temperatureT₂ with respect to initial temperature level T₁ is a result of, that aheat stream—not shown—in the ORC arrangement as per FIG. 1 betweenturbine 7 that is shown there and recuperator 8 that is shown there, aheat exchanger—not shown—is used to heat the cold side 23 of heattransformer 21, whereby the second heat stream that is extracted at anexpansion temperature level is pumped to a pump temperature level abovethe initial temperature level T₁.

In an embodiment of the process, condenser 9 and recuperator 8 that areshown in FIG. 1 can also be omitted so that working fluid 6—after theturbine—is heated for extraction of the second heat stream by the—notshown—heat exchanger and is conveyed from there to the pre-heater.

Downstream of ORC cycle 20, the low-temperature mass stream has atemperature T₃. This temperature is lower than the first temperaturelevel T₁ as well as the second temperature T₂.

In place of ORC cycle 20, in an embodiment according to the inventionthat is not shown, a Kalina cycle can also be used.

The following table shows exemplified calculations for salt-containingbrine with a salt content of 100 g per liter as low-temperature massstream 1. The low-temperature mass stream 1 is indicated in the firstcolumn as delivery in I/s and the density of the brine is 1077.84 kg/m³.For reasons of clarity, however, only the volume streams are indicated.The inlet temperature and thus the initial temperature level T₁ is 120°C., as shown in column 2. The outlet temperature T₃ is 75° C., as shownin column 3. The heat capacity of the brine of 3.2 kJ/(kgK) results inthermal output as shown in column 4. When a degree of effectiveness ofthe power plant is assumed as indicated in column 5, electrical outputresults as shown in column 6. Use of a heat transformer 21, which pumpsthe second heat stream to the higher pump temperature level of 160° C.after it has been extracted from working fluid 6 subsequent to expansionin the turbine, leads—assuming waste heat of 20%—to an output of asecond heat stream as per column 7. Assuming that this second heatstream after it is pumped to 160° C. at a loss of 10% is input into thelow-temperature mass stream, input heat as per column 8 results, whichleads to a temperature increase of low-temperature mass stream 1 as percolumn 9 of 6.34 K, at a degree of effectiveness of 12% for the powerplant. Thus an improvement of the electrical effectiveness of thelow-temperature power plant of 14.1% is the result.

For other waste heat that is dissipated by the heat transformer, othervalues are attained respectively. For example, at a delivery of 100 I/sand a degree of effectiveness of the power plant of 12% at waste heat of25%, a temperature increase of the low-temperature mass stream 1 of7.92K results and an improvement of the degree of effectiveness of thelow-temperature power plant of 17.6%.

At a delivery of 100 I/s when the power plant has a degree ofeffectiveness of 12% and waste heat of 30% a temperature increase of9.5K results and an improvement of the degree of effectiveness of thelow-temperature power plant of 21.1%.

Delivery Inlet Outlet Thermal KW Electrical Output Input TemperatureIncrease in in Temp. in Temp. in output in effectiveness output in heatin heat in increase in effectiveness l/s ° C. ° C. kW in % kW kW kW ° C.% 50 120 75 7,760 12 931 1,366 1,093 6.34 14.1% 100 120 75 15,521 121,863 2,732 2,185 6.34 14.1% 150 120 75 23,281 12 2,794 4,098 3,278 6.3414.1% 50 120 75 7,760 14 1,086 1,335 1,068 6.19 13.8% 100 120 75 15,52114 2,173 2,670 2,136 6.19 13.8% 150 120 75 23,281 14 3,259 4,004 3,2046.19 13.8% 50 120 75 7,760 16 1,242 1,304 1,043 6.05 13.4% 100 120 7515,521 16 2,483 2,608 2,086 6.05 13.4% 150 120 75 23,281 16 3,725 3,9113,129 6.05 13.4%

In the variant shown in FIG. 4, in addition to a first ORC cycle 20, asecond ORC cycle 25 is provided, which is located sequentiallydownstream of first ORC cycle 20 relative to a low-temperature massstream 1. Further, a first heat transformer, 21, as well as a secondheat transformer 26 is provided which have a heat stream connection withlow-temperature mass stream 1 with their warmer sides 22 respectively.In turn, the cold sides 23 of the heat transformers are located, as inthe previous example of an embodiment as per FIG. 3, down-stream of theturbine. The second heat flows extracted from the waste gas streams ofthe turbine respectively at an expansion temperature level, are pumpedrespectively to a higher pump temperature level in first heattransformer 21 or in second heat transformer 26. As a result of acorresponding location of first heat exchanger 24 and a second heatexchanger 27, a step-wise temperature increase of the firstlow-temperature mass stream 1 downstream of first ORC cycle 20 can beprovided from a temperature T₂ to a temperature T₃ and then subsequentlyto a temperature T₄. Thereby in turn, temperature T₁ is lower than theinitial temperature level T₁, whereby temperature level T₅, at whichlow-temperature mass stream 1 exits again downstream of the second ORCcycle 25, is lower than temperature T₄.

By using the previously mentioned brine as low-temperature mass stream,at an initial temperature level T₁ of 120° C. and an exit temperature T₅of 75° C., the following values result for temperatures T₂, T₃ and T₄,whereby the higher pump temperature level of the first and second heattransformer is respectively 160° C. and 20% of the waste heat of theturbine is dissipated by the heat transformers at a loss of 10%:T₂=97.5° C., T₃=T₂+3.96° C., T₄=T₂+3.96° C.+4.26° C. Thereby, the degreeof effectiveness of the overall system is improved by 11.2%.

In a variant according to FIG. 5, a first ORC cycle 20 and a second ORCcycle 25 are provided, whereby a branch stream 28 is branched off fromlow-temperature mass stream 1 downstream of first ORC cycle 20, wherebya heat exchanger 24 is provided which has a heat stream connection witha warm side 22 of a heat transformer 21, and thus heats a mass streamdm₂/dt from a temperature T₂ to a temperature T₃. A cold side 23 of heattransformer 21 is thereby in turn, as in the previously describedembodiments, brought in contact with a working fluid of first ORC cycle20 downstream of a turbine. The second heat stream that is extractedthereby is pumped by a heat transformer 21 to a temperature abovetemperature T₂, so that the mass stream dm₂/dT can be heated fromtemperature T₂ to temperature T₃. This heated mass stream dm₂/dt at atemperature T₃ is used for the operation of second ORC cycle 25. Anoutflow 29 downstream of second ORC cycle 25 is fed again—downstream ofthe first ORC cycle 20—into first low-temperature mass stream 1.

Thereby, the outflow shows a temperature T4, which is larger than T₅,which is shown by low-temperature mass stream 1 at the end. Moreover,temperature T₃ is higher than temperature T₂.

By using the brine that was already presented as low-temperature massstream, the following values result in an exemplified calculation.Thereby, a branch stream 28 is provided as per partial deliveryaccording to column 6. The second heat stream which is extracted by heattransformer 21, also amounts to 20% of the heat carried in the outflowfrom the turbine. This second heat stream is given off again at a lossof 10% by the heat transformer after being pumped to the higher pumplevel. The input temperature and thus the initial temperature level is120° C., the exit temperature T₅ is 75° C. Thereby, temperatures T₂ andT₄ are approximately identical to temperature T₅.

Delivery Inlet Outlet Thermal Degree of Electrical output PartialElectrical energy Increase in in Temp. in Temp. in output ineffectiveness in in KW effectiveness delivery in creation ineffectiveness l/s ° C. ° C. kW % 12% l/s KW % 50 120 75 7,760 12 9319.50 177.01 19.0% 100 120 75 15,521 12 1,863 19.01 354.03 19.0% 150 12075 23,281 12 2,794 28.51 531.04 19.0% 50 120 75 7,760 14 1,086 9.29201.82 18.6% 100 120 75 15,521 14 2,173 18.58 403.64 18.6% 150 120 7523,281 14 3,259 27.86 605.46 18.6% 50 120 75 7,760 16 1,242 9.07 225.2918.1% 100 120 75 15,521 16 2,483 18.14 450.58 18.1% 150 120 75 23,281 163,725 27.22 675.87 18.1%

One possibility of separately streaming cycles is shown in FIG. 6.Thereby, a first ORC cycle 20 and a second ORC cycle 25 are onlyconnected by a heat transformer 21, whereby the warm side 22 of the heattransformer supplies a heat exchanger 24 with a heat stream. This heatstream is fed to a low-temperature mass stream 1, which, via adownstream feedback 29 a is again conveyed to an inlet 29 b of ORC cycle20 and thus is continuously circulated. The heat stream supplied to heattransformer 21 is extracted downstream of first ORC cycle 20 fromoutflow 29.

In a modified arrangement according to FIG. 7, heat exchanger 24,contrary to the embodiment in FIG. 6, is not downstream of first ORCcycle 20, but located in this first ORC cycle 20. Heat exchanger 24 isthereby provided next to or instead of a condenser.

In the variant shown in FIG. 8, no temperature increase of alow-temperature mass stream 1 is undertaken instead, thislow-temperature mass stream 1 is increased by partial recirculation 30.For this purpose, a branch stream 28 is branched off from thelow-temperature mass stream 1 downstream of an ORC cycle 20, which runsthrough a heat exchanger 24 that is fed by the warm side 22 of heattransformer 21. A cold side 23 of heat transformer 21 is in turnconnected with ORC cycle 20 in the way it was previously described. Inheat exchanger 24, branch stream 28 dm₃/dt is heated from a temperatureT₂ to a pump temperature level T₁, which precisely corresponds to theinitial temperature level T₁ of the low-temperature mass stream 1. Inthis manner, a comparison to the originally present mass streamdm₁/dt+dm₃/dt results. Simultaneously, the mass stream flowingdownstream is only dm₁/dt.

The following values are in turn calculated for brine as alow-temperature mass stream with an initial temperature level of 120° C.as inlet temperature. The branch stream is set as per the partialdelivery shown in column 7. As pump temperature level of the second heatstream, 160° C. is provided, whereby heat transformer 21 pumps 20% ofthe waste heat of the turbine to pump temperature level with a degree ofeffectiveness of 90%.

Delivery Inlet Outlet Thermal KW Electrical Partial Increase in in Temp.in Temp. in output in effectiveness performance in delivery ineffectiveness l/s ° C. ° C. kW in % kW l/s % 50 120 75 7,760.45 12931.25 9.50 19.0% 100 120 75 15,520.90 12 1,862.51 19.01 19.0% 150 12075 23,281.34 12 2,793.76 28.51 19.0% 50 120 75 7,760.45 14 1,086.46 9.2918.6% 100 120 75 15,520.90 14 2,172.93 18.58 18.6% 150 120 75 23,281.3414 3,259.39 27.86 18.6% 50 120 75 7,760.45 16 1,241.67 9.07 18.1% 100120 75 15,520.90 16 2,483.34 18.14 18.1% 150 120 75 23,281.34 163,725.02 27.22 18.1%

In the arrangement shown in FIG. 9, a working fluid 6 is brought to ahigher temperature level directly prior to a turbine 7 by a heattransformer 21. In detail, this is again an ORC cycle in which alow-temperature mass stream 1 heats a vaporizer 5 at an initialtemperature level, whereby working fluid 6 is vaporized and after anadditional heating by a warm side 22 of heat transformer 21 is fed toturbine 7. There, an expansion takes place on account of which work isperformed that is transformed into electrical energy by an electricgenerator 31. After exiting turbine 7, expanded working fluid 6 issupplied to a heat exchanger 24, which has a heat stream connection witha cold end 23 of heat transformer 21. As a result, from expanded workingfluid 6 exiting the turbine at an expansion temperature T₅, a secondheat stream is extracted which is being pumped to a pump temperaturelevel above temperature T₃ with the help of heat transformer 21. Thus,temperature T₄ prior to entering turbine 7 is above temperature T₁ oflow-temperature mass stream 1 in the vaporizer.

The following values are in turn calculated for brine as low-temperaturemass stream at an initial temperature level T₁ of 120° C. as inlettemperature. As pump temperature level of the second heat stream, 160°C. is provided, whereby heat, transformer 21 pumps 20% of the waste heatof the turbine to pump temperature level with a degree of effectivenessof 90%. The outlet temperature T₅ is 75° C.

Delivery Inlet Oulet Thermal KW Electrical Output Input Increase in inTemp. in Temp. in output in effectiveness output in heat in heat ineffectiveness l/s ° C. ° C. kW in % kW kW kW % 50 120 75 7,760 12 9311,366 1,093 14.1% 100 120 75 15,521 12 1,863 2,732 2,185 14.1% 150 12075 23,281 12 2,794 4,098 3,278 14.1% 50 120 75 7,760.45 14 1,086.461,334.80 1,067.84 13.8% 100 120 75 15,520.90 14 2,172.93 2,669.592,135.68 13.8% 150 120 75 23,281.34 14 3,259.39 4,004.39 3,203.51 13.8%50 120 75 7,760.45 16 1,241.67 1,303.76 1,043.00 13.4% 100 120 7515,520.90 16 2,483.34 2,607.51 2,086.01 13.4% 150 120 75 23,281.34 163,725.02 3,911.27 3,129.01 13.4%

REFERENCE Numbers

-   -   1 Low-temperature mass stream    -   2 deep well pump    -   3 geothermal source    -   4 first heat exchanger    -   5 vaporizer    -   6 working fluid    -   7 turbine    -   8 recuperator    -   9 condenser    -   10 fee pump    -   11 pre-heater    -   12 desorber    -   13 separator    -   14 steam phase    -   15 watery phase    -   16 high temperature recuperator    -   17 constrictor    -   18 low-temperature recuperator    -   19 absorber    -   20 first ORC cycle    -   21 first heat transformer    -   22 warm side of heat transformer    -   23 cold side of heat transformer    -   24 (first) heat exchanger    -   25 second ORC cycle    -   26 first heat transformer    -   27 second heat transformer    -   28 branch stream    -   29 outflow    -   29 a downstream recirculation    -   29 b inlet (of ORC cycle)    -   30 partial recirculation    -   31 electric generator

1. Thermodynamic machine, particularly a low-temperature power plant,with at least one first cycle (20) for circulating a working fluid,whereby the first cycle (20) has at least one expansion machine (7) andat least one heat exchanger (24; 27) for feeding a first heat streamfrom a low-temperature mass stream (1) into the first cycle (20),whereby a first heat transformer (21; 26) is provided in heat streamconnection with the first cycle (20), with a colder side (23) downstreamof the expansion machine (7), and has a heat stream connection with awarmer side (22) with the low-temperature mass stream (1) or the firstcycle (20).
 2. Thermodynamic machine according to claim 1 furthercomprising a second cycle (25), particularly an ORC cycle, with a secondheat transformer (26), which is located in the same way as the firstheat transformer (21), sequentially to the first cycle (20), whereby thefirst (21) and the second heat transformer (26) respectively have a heatstream connection with the low-temperature mass stream (1) between thefirst (20) and the second cycle (25) with their warmer side (22). 3.Thermodynamic machine according to claim 1 further comprising a secondcycle (25) that is fed by a branch stream (28) by the low-temperaturemass stream (1) downstream of the first cycle (20), whereby the firstheat transformer (21) with its warmer end (22) has a heat streamconnection with the branch stream (28) upstream of the second cycle(25), and whereby a downstream feedback of the branch stream (28) isprovided downstream of the second cycle (25) into the low-temperaturemass stream (1).
 4. Thermodynamic machine according to claim 1 furthercomprising a second cycle (25) that has a downstream feedback (29 a) toan inlet (29 b), which has a heat stream connection with the warmer end(22) of the first heat transformer (21).
 5. Thermodynamic machineaccording to claim 1 further comprising at least one recirculation line(30) provided for feedback of a branch stream (28) of thelow-temperature mass stream (1) downstream of the first cycle (20),whereby the warm side (22) of the first heat transformer (21) has a heatstream connection with the branch stream (28).
 6. Thermodynamic machineaccording to claim 1 wherein the warm side (22) of the first heattransformer (21) in a section between a vaporizer (5) and expansionmachine (7) has a heat stream connection with the first cycle (20). 7.Process for operating a thermodynamic cycle, particularly in alow-temperature power plant according to claim 1, with at least onecycle (20, 25), in which a working fluid (6) circulates, to which afirst heat stream is fed by a low-temperature mass stream (1) at aninitial temperature level, whereby after an expansion of the workingfluid (6) in an expansion machine (7) releasing mechanical energy asecond heat stream is extracted from the working fluid (6) at anexpansion temperature level that is lower compared to the initialtemperature level wherein the second heat stream in at least one heattransformer (21, 26) is pumped to a pump temperature level which ishigher or equal to the initial temperature level and is at leastpartially fed back to low-temperature mass stream (1) and/or the atleast one cycle (20, 25).
 8. Process according to claim 7 wherein thesecond heat stream, which is raised to the pump temperature level,increases a temperature of the low-temperature mass stream (1) and/or atemperature of the working fluid (6) in the at least one cycle (20, 25).9. Process according to claim 7 wherein the low-temperature mass stream(1) is increased by a partial feedback of a low-temperature mass streamoutflow (29) that is heated by the second heat stream.
 10. Processaccording to claim 7, wherein at least one cycle (20, 25) is operated asan organic Rankine cycle (ORC).
 11. Process according to claim 7 whereinthe at least one cycle (20, 25) is operated as a Kalina cycle. 12.Process according to claim 7 wherein at least two cycles, particularlytwo ORC cycles (20; 25), are sequentially fed by the low-temperaturemass stream (1), whereby a feedback into the low-temperature mass stream(1) of the second heat streams of the cycles that is pumped to therespective pump temperature level takes place between the first cycle(20) and the second cycle (25).
 13. Process according to claim 7 whereinat least two cycles (20, 25), particularly two ORC cycles, are provided,whereby from the low-temperature mass stream (1) downstream of the firstcycle (20) a branch stream (28) for feeding a second cycle (25) isbranched off, which downstream of the second cycle (25), is reuniteddownstream with the low-temperature mass stream (1), whereby the secondheat stream that is pumped to the pump temperature level of the firstcycle (20) is fed to the branch stream (29).
 14. Process according toclaim 7 wherein at least two cycles (20, 25), particularly two ORCcycles are provided, whereby the second heat stream of the first cycle(20) that is pumped to the pump temperature level is fed to an outflowof the second cycle (25), which is fed again to the second cycle (25) asinflow.
 15. Process according to claim 7 wherein a branch stream (28) isbranched off from the low-temperature mass stream (1) downstream of acycle (20), which is heated by the second heat stream to the pumptemperature level and is fed to the low-temperature mass stream (1)upstream of the cycle (20).
 16. Process according to claim 15 whereinthe branch stream (28) is dimensioned in such a way, that its pumptemperature level prior to recirculation corresponds to the initialtemperature level of the low-temperature mass stream (1).
 17. Processaccording to claim 7 wherein the second heat stream is extracteddownstream of the expansion machine (7) and after being pumped to thepump temperature level, is fed back into the cycle (20), particularlydirectly before the expansion machine (7).
 18. Process according toclaim 7 wherein a temperature of a heat transformer fluid is heated bythe second heat stream and raised by at least two ejector-adsorbers toor above the pump temperature level to pump the second heat stream tothe pump temperature level.
 19. Process according to claim 7 wherein aheat transformer fluid heated by a second heat stream is at leastessentially adiabatically compressed and thereby heated to or above thehigher pump temperature level to pump the second heat stream to pumptemperature level.
 20. Thermodynamic machine, according to claim 1, withthe at least one heat transformer (21; 26) being configured such thatfrom a first mass stream with a first temperature level a second massstream with a second temperature level is produced with the second massstream being equal or less than the first mass stream and with thesecond temperature level being higher than the first temperature level.